1. Field of the Invention
The invention relates to a method for the deep drawing of a metal sheet by means of a press, a table, a drawing punch, and also a drawing die and a counterpressure plate interacting with the drawing die, which together form a flow path for the metal sheet, wherein at least one drawing strip movable relative to the counterpressure plate is pushed transversely through the flow path of the metal sheet in order to deflect the metal sheet during a drawing phase (first deflection phase) and the drawing strip, for a stop phase, is pushed by a further short distance transversely through the flow path (second deflection stage), wherein a deflection increased once again inhibits the flow of the metal sheet during the second deflection stage, and wherein the metal sheet is essentially plastically formed at the end of the deep-drawing operation.
The flow path is a drawing gap formed between a drawing die and counterpressure plate. The metal sheet slips through this drawing gap, in the course of which it is inhibited by the pressure of the counterpressure plate.
The invention also relates to a deep-drawing apparatus for metal sheets, comprising a table, a drawing punch, a press, a drawing die, a counterpressure plate, a plurality of drawing strips which are mounted in the counterpressure plate such as to be movable parallel to the press direction of the press, and drawing grooves which are provided at the margin of the drawing die and into which the drawing strips can be moved step by step while maintaining a drawing gap, a drawing phase being provided for the purpose of step-by-step forming of the metal sheet, during which the drawing phase of the metal sheet is given a drawing bead having a small bead depth, and at least one stop phase being provided, during which the metal sheet is given a stop bead which has a larger bead depth than the drawing bead.
Normally used for the production of car body parts are very large mechanical or hydraulic presses with counterholding devices which essentially have to ensure exact adjustability of the press force and counterholding force, since different drawn parts require different press forces and counterholding forces. The counterholding devices can be designed in a wide variety of ways; in this case the counterholding force is preferably applied hydraulically or by spring force.
The press and the counterholding device deliver the forces which are required for the forming. In addition, a deep-drawing apparatus is required which has individual forming tools, such as a drawing punch, drawing die and individual devices for controlling the material flow.
2. Description of Related Art
A method of the generic type for the deep drawing of metal sheets and a deep-drawing apparatus are known from U.S. Pat. No. 6,276,185 B1. In this case, the material flow is controlled by two drawing strips which are arranged symmetrically relative to a drawing punch. The drawing strips are pushed transversely into the flow path of the metal sheet in order to meter the material flow. This first deflection stage is maintained until the bottom ends of the drawing strips, which project freely from the counterpressure plate, strike a table. Starting from this instant, the drawing strips are pushed further through the flow path of the metal sheet, as a result of which the flow process is further inhibited.
A disadvantage of this prior art is the lack of variability of the deep-drawing apparatus. The known deep-drawing apparatus can be changed over or set only in a very complicated manner if the adjustment of the setting becomes necessary.
Another deep-drawing apparatus is known from German Patent No. DE 199 53 751 A1. Said deep-drawing apparatus proposes drawing strips which are to be moved via mechanical transmissions or hydraulic circuits, although provision is not made for the drawing strips to be moved in two steps transversely through the flow path for a drawing phase and a stop phase. The measures known from German Patent No. DE 199 53 751 A1 for driving the drawing strips are complicated and susceptible to damage and therefore appear to be less suitable in particular for mass production, as in the automobile industry for example.
The object of the invention is to propose a method for the deep drawing of metal sheets which ensures an exact consistent deflection of the flow path of the metal sheet during the drawing phase, great importance being attached to simple and quick adjustability in order to vary the degree of deflection if a fine adjustment, i.e. in the event of wear of the tool or when the material characteristics are changed, becomes necessary.